Peter Foster is the Telegraph's US Editor based in Washington DC. He moved to America in January 2012 after three years based in Beijing, where he covered the rise of China. Before that, he was based in New Delhi as South Asia correspondent. He has reported for The Telegraph for more than a decade, covering two Olympic Games, 9/11 in New York, the 2004 Boxing Day tsunami, the post-conflict phases in Afghanistan and Iraq and the 2011 Fukushima disaster in Japan.

Syria: why Obama could still win his vote in Congress

Barack Obama has today framed the fundamental question that Congressmen will face when they vote on whether to authorise the use of force in Syria.

He concedes in advance that he may not carry public opinion with him – US intervention overseas, he argues, is always unpopular. It was in World War II before Pearl Harbour and it was in Kosovo.

But even if the public is not supportive, and we know it is not, members of Congress will still have to decide whether to support their president's judgment that US national security and standing is at stake.

They key passage is here:

It's conceivable that, at the end of the day, I don't persuade a majority of the American people that it's the right thing to do.

And then each member of Congress is going to have to decide if I think it's the right thing to do for the — America's national security and the world's national security, then how do I vote? And you know what? That's — that's what you're supposed to do as a member of Congress.

Ultimately, you listen to your constituents, but you've got to make some decisions about what you believe is right for America.

Framed that way, to say "no" to that request would be a very, very major step for Congress, which is genuinely agonising over this vote, partisan politics to one side. The White House hopes that the starkness of this choice will win the day for Mr Obama in the end.

The alternative, particularly for wavering Democrats, is to leave their president winged for the rest of his presidency.

For Republicans, particularly those who foresee the need to confront the threat of Iran in coming years, the risk is that a "no" vote would weaken the executive authority of the commander-in-chief, now and in the future.

Mr Obama might still lose this vote, but this is why I would argue – and several House and Senate aides we have spoken to also argue – when the showdown comes it will be a much closer vote than the headline numbers currently suggest.